1. Field of the Invention
The present disclosure relates to a method of detecting the misalignment of ion implantation areas of a semiconductor device and, more particularly, to a method of determining the misalignment of ion implantation areas immediately after an ion implantation process is completed.
2. Background of the Related Art
A complementary metal oxide semiconductor (hereinafter referred to as “CMOS”) device comprises an N-MOS transistor and a P-MOS transistor which are formed within the same semiconductor substrate. Either N-MOS transistor or P-MOS transistor must be formed on an impurity region which has a different conduction type from that of substrate in order to separate electrically the N-MOS transistor from the P-MOS transistor on the semiconductor substrate. Particularly, the impurity region is called a well.
The well is generally created through a dopant ion implantation process, a lengthy thermal treatment process at a high temperature, and a diffusion process to diffuse the implanted dopant to an appropriate depth. This well is particularly known as a diffusion well. In addition to the diffusion well, various well structures have been developed to simplify a well formation process and to improve well functions. For example, a retrograde well is made by performing a high-energy ion implantation process to locate dopants at an appropriate depth after a device isolation structure is formed on a silicon substrate.
In making those well structures, it is very important to implant exactly n-type and p-type dopants into predetermined places within a silicon substrate and to align precisely n-type and p-type wells. If in fabricating a CMOS device the n-type and p-type wells are misaligned on the silicon substrate, devices such as transistors and capacitors, which are formed on the silicon substrate based on the p-type and n-type wells, may not properly function due to several problems such as leakage current.
A conventional well formation process is described to illustrate examples of misalignment of ion implantation areas. FIGS. 1a through 1c show, in cross-sectional views, a known process of forming n-type and p-type wells.
Referring to FIG. 1a, first, device isolation structures 102 are formed on a p-type semiconductor substrate 101 by a local oxidation of silicon (hereinafter referred to as “LOCOS”) or a shallow trench isolation (hereinafter referred to as “STI”) process so as to define active regions and field regions of a semiconductor device. A first ion implant mask 103 is then formed over the semiconductor substrate 101 by using photoresist. The first ion implant mask 103 exposes the some active regions of the semiconductor substrate on which a p-type well will be formed.
Referring to FIG. 1b, a p-type ion implantation process is performed for the semiconductor substrate 101, thereby forming a p-type ion implant layer 104 with a predetermined depth on the silicon substrate.
Referring to FIG. 1c, the first ion implant mask 103 is removed. Next, a photoresist layer is deposited over the semiconductor substrate 101 and a second ion implant mask 105 is patterned through exposure and development processes. The second ion implant mask 105 exposes other active regions on which an n-type well will be formed. An n-type ion implantation process is then performed for the semiconductor substrate 101, thereby forming an n-type ion implant layer 106 with a predetermined depth on the semiconductor substrate.
A thermal treatment process is then performed for the resulting substrate having n-type and p-type ion implant layers so that the ions in the n-type and p-type ion implant layers are diffused into the semiconductor substrate to complete n-type and p-type wells.
In the conventional well formation process, to form n-type and p-type wells ion implant masks are required. Each ion implant mask must be exactly positioned over the predetermined region of either an n-type or a p-type well. If the ion implant mask is misaligned, n-type or p-type impurity ions may not be implanted into the predetermined region.
Such misalignment may occur during an ion implantation process to define source/drain regions. For example, a device isolation structure is formed on a semiconductor substrate to define an active region. A gate electrode pattern is then formed on a predetermined position within the active region. And an n-type or p-type ion implantation process is carried out over the semiconductor substrate having the gate electrode pattern. Here, the ions implanted into a source/drain region within a first active region may have a different conduction type from the ions implanted into a source/drain region within a second active region adjacent to the first active region. For example, the ions implanted into a source/drain region within the first active region may be first conduction type impurity ions and, on the other hand, the ions implanted into a source/drain region within the second active region adjacent to the first active region may be second conduction type impurity ions. To form source/drain regions by implanting selectively the first and second conduction type ions into a plurality of active regions divided by device isolation structures, predetermined ion implant masks are required. Accordingly, misalignment may occur during ion implantation processes as stated in the above well formation process.
The misalignment in making source/drain regions is described in more detail referring to FIGS. 2a through 2i. 
Referring to FIG. 2a, device isolation structures 202 are formed on a semiconductor substrate 201 to define a plurality of active regions. Next, n-type and p-type impurity ions are selectively implanted to form at least one source/drain region within each active region. Here, in order to implant specific conduction type ions only into a predetermined region, an ion implant mask with an appropriate pattern must be used so that regions in which opposite conduction type ions will be implanted can be protected. FIG. 2a illustrates, in a cross-sectional view, an ion implant configuration without misalignment due to correct disposition of the ion implant mask.
FIG. 2b illustrates, in a cross-sectional view, an example of a misaligned ion implant configuration. In FIG. 2b, each ion implant mask to implant n-type and p-type ions leaned to the right from a normal location before ion implantation processes were performed. In this case, if the semiconductor substrate is a p-type, there is no problem. However, if the semiconductor substrate is an n-type, leakage current may occur.
FIG. 2c shows, in a cross-sectional view, another example of a misaligned ion implant configuration. In FIG. 2c, an n-type ion implant mask leaned to the right and a p-type implant mask leaned to the left before ion implantation processes were performed. Both n-type impurities and p-type impurities were implanted into some areas on both sides of the device isolation area. In this case, if the silicon substrate is an n-type, leakage current occurs. If the silicon substrate is a p-type, a little leakage current may occur.
FIG. 2d illustrates, in a cross-sectional view, a third example of a misaligned ion implant configuration. In FIG. 2d, an n-type ion implant mask leaned to the left and a p-type ion implant mask leaned to the right before ion implantation processes were performed. In this case, leakage current will necessarily occur regardless of the conduction type of the silicon substrate.
FIGS. 2e through 2i also show, in cross-sectional views, other examples of misaligned ion implant configurations that may be occurred during the source/drain region formation. The misalignments illustrated in FIGS. 2a through 2i, may also appear during the well formation process.
In fabricating a CMOS device, the processes for forming wells and source/drain regions are carried out relatively at early stages during semiconductor fabrication. Therefore, if defects occur during the well or source/drain region formation and the later processes are performed without detection of the defects, the resulting devices will be defective whether the later processes are done with or without defects.
Semiconductor manufacturing generally comprises a fabrication process, an assembly process, and a test process. So, the defects of a semiconductor device with misaligned wells or source/drain regions are detected during the final test for the semiconductor device. As a result, to perform later processes and tests for the semiconductor device with defects due to misalignment of ion implantation areas may be a waste of time and increase production costs.